This research program is concerned with the exploration of the various mechanisms of interaction between the neural and the endocrine integrative centers of insects. Special attention is being directed to the efferent link which encompasses control over non-neural endocrine organs such as the corpus allatum by conventional as well as non- conventional neurochemical signals. Among the latter, the choice is between neurohormonal (bloodborne) and intermediate, i.e., close range commands, both of which make use of chemical mediators that are not of the orthodox neurotransmitter type, but belong to a special class of neurosecretory peptidergic neuronal products. The comparative functional interpretation of sites of release for these diverse messenger substances (synapses and synaptoid structures) continues to be of interest in terms of the elucidation of general principles. The role of the extracellular stromal element which intervenes between many of the endocrine effector cells and the axons by which the messenger substances are conveyed will be further examined at various stages by means of tracer substances. Another important link between these interacting organs are hemocytes. Their participation in the expression of the programmed activity cycles of the endocrine system and their mode of differentiation will be examined in as many diverse species as possible.